Process and apparatus for the manufacture of phosphorous acid



Dec." 10, 1968 REMER ETAL 3,415,624

PROCESS AND APPARATUS FOR THE MANUFACTURE OF PHOSPHOROUS ACID Filed Aug. 6, 1965 United States Patent 3,415,624 PROCESS AND APPARATUS FOR THE MANU- FACTURE 0F PHOSPHOROUS ACID Joseph Cremer, Hermulheim, near Cologne, Ursus Thummler and Friedrich Schulte, Hurth, near Cologne, and Heinz Harnisch, Lovenich, Weiden, Germany, assignors to Knapsack Aktiengesellschaft, Knapsack, near Cologne, Germany, a corporation of Germany Filed Aug. 6, 1965, Ser. No. 477,715 Claims priority, application Germany, Sept. 19, B64, K 540,461 6 Claims. (Cl. 23-165) ABSTRACT OF THE DISCLOSURE Apparatus and process for the manufacture of phosphorous acid from phosphorus trichloride and water by hydrolysis comprising introducing phosphorus trichloride and water as the starting components in finely divided form into a reaction zone, intimately mixing the components, reacting the components in the gas phase at a temperature of 150 to 200 C., and removing resulting final product in the form of a melt.

The present invention provides a one-stage process for the manufacture of H PO by hydrolyzing PO1 It is known that H PO can be produced by hydrolyzing PCl The reaction incurs difficulties which are produced by the poor miscibility of the reactants and by the considerable amount of reaction heat set free once the reaction has started.

In order to reduce such difiiculties, it has been attempted, for example, to admix P01 with CCL, and slowly to add water to the mixture so as to allow the hydrolysis to take place in dilute material and hence under mild thermal conditions. This process did not gain commercial interest for the reason that elevated throughputs call for a large volume of liquid and for the reason that crude H PO is a product difficult to purify.

In order to improve mixing and to accelerate the reaction, it is suggested in another known process that PC1 and an excess of water of 3.6 to 4.2 mols H O per mol PO1 be introduced into a reactor which is charged with H PO HCl and Water and provided with a cooling coil. In this process, the reaction is generally carried out at a temperature of 50 to 60 C. Mixing of the reactants in the reactor sump portion is achieved by means of HCl-gas bubbles which ascend in the liquid.

A still further conventional process aims at obviating cooling. Stoichiornetric proportions of PCl water and steam are introduced in measured quantities into a reactor which is charged with H PO H 0 and HCl and which is designated so as to enable the material in the reactor sump portion to be circulated in the liquid reactor by means of gas bubbles ascending and by means of the differential temperatures prevailng therein. In this process, the reaction temperature is at about 75-200 C. and some heat exchange is likely to occur at the reactor walls.

In a still further process, PCl is metered into a sump of reaction material consisting of H PO H 0 and HCl and partially hydrolyzed therein. PCl i.e. about 40% of the quantity introduced, which is evaporated by the reaction heat set free is hydrolyzed in the gas phase. A

3,415,624 Patented Dec. 10, 1968 stoichiometric proportion of water is added at the head portion of the apparatus counter-currently to PO1 in vapor form. This process employs no cooling means and the desired temperature is produced by heating the liquids chamber and the gas chamber.

In the above process, crude acid such as withdrawn from the reactor sump portion must always be freed in a second step from H 0 and hydrochloric acid at a temperature of to C. by causing an inert gas to flow therethrough or by evacuation.

The disadvantages associated with the processes described above accrue from the difliculties mentioned above and encountered on hydrolyzing PCl Liquid PCIg, when cold, reacts very reluctantly with water. The two reactants difier in density and therefore produce two phases so that hydrolysis sets in reluctantly near the two phases boundary surface only. Allowing the material to stand for a period long enough or agitating and/or heating it results in the reaction setting in at once which may become so violent that the decomposition temperature of H3P03 (200 C.) is reached or even exceeded due to local superheating.

In order to avoid these two kinds of diiiiculties, i.e. too low a reaction velocity and superheating, the above processes always introduce PCl into a sump of reaction material consisting of H PO HCl and H 0 since the hydrolysis takes place in such medium at a tolerable reaction velocity. HClagas bubbles such as set free during the reaction are used for stirring up the sump to achieve the necessary mixing of the reactants which include PCl and water, to achieve heat distribution concurrently therewith and optionally to achieve heat dissipation through a cooling coil or the reactor walls.

The large volume of liquid, which must necessarily be used for large throughputs to achieve complete hydrolysis within a reasonable period and to achieve heat distribution or heat dissipation renders this process unsatisfactory and uneconomic.

The production of pure phosphorus acid, which must necessarily be prepared from the reaction sump, is more especially an uneconomic procedure. Removing the partially considerable amounts of H 0 and HCl from crude H PO always calls in these processes for a second treatment step which comprises evacuating the crude acid or passing an inert gas therethrough at a temperature of 100 to 150 C. to concentrate the crude acid so as to obtain pure H PO The present invention now provides a simple process for making H PO by hydrolyzing phosphorus trichloride and water, wherein the starting components are introduced in finely divided form into a reaction chamber, intimately mixed therein, reacted in the gas phase at a temperature of 150 to 200 C. preferably of to C., and the resulting final product is withdrawn in the form of a melt. Intimate mixing of the reaction components which are used, e.g. in the form of an aerosol, re sults in a high reaction velocity, which enables relatively small reaction spaces to be employed. As opposed to conventional methods, the present invention offers the further advantage of obviating using any additional volume for crude acid otherwise necessary to achieve the reaction, i.e. of obviating the reaction sump.

The process of the present invention even enables the hydrolysis to be carried out at a temperature approaching the temperature at which H PO undergoes thermal decomposition (200 C.) provided that exothermal reaction heat initiating the decomposition is dissipated at least partially in the form of heat of evaporation for PCl and water.

The temperatures at which the reaction shall take place can be adjusted and regulated by injecting the water in drop, mist or vapor form into the reactor at an appropriate low temperature. The water is optionally used in an excess related to the amount theoretically necessary to hydrolyze PCl A temperature range of 150-200" C., preferably 160 190 C., is most conveniently used for causing the PC1 to react instantaneously with water and for rapidly expelling water and hydrochloric acid from the resultant H PO It has also been found that the reaction velocity can be varied within wide limits by the size of the PCl -droplets.

For example, the reaction takes an explosion-like course when the PCl -droplets have a mean size smaller than 50g (mist) and when a slight excess of steam is used, whereas seconds or minutes are necessary to achieve the reaction when the droplets have a mean size greater than 500a. PCl -droplets having a mean size greater than 50p and less than 500p are most conveniently used.

The starting components are advantageously atomized by means of an inert gas, e.g. air, nitrogen or CO Following the reaction, residual H and HCl are expelled at about the same temperature as indicated above from the reaction product by evaporation and/or by means of an inert gas, e.g. air, nitrogen or CO To expel residual hydrochloric acid and water, the H PO -melt which deposits in the vapor space on the reactor walls is allowed to travel through a heated evaporator into which air, N or CO is injected in conventional manner. The H PO -melt which is continuously discharged through an overflow solidifies on being cooled and inoculated.

The products prepared in accordance with the present invention contain C1 in a proportion less than 0.05%, P0; in a proportion less than 1.4%, and H 0 in a proportion less than 1.5%.

An apparatus suitable for use in carrying out the process of the present invention is shown diagrammatically in the accompanying drawing. It is made of material resisting to hydrochloric acid, e.g. glass, ceramics, Diabon or graphite.

The apparatus comprises a reaction chamber 1 which has feed pipes 2, 3 and 4 supplying and means distributing the reaction components, a series-connected evaporator 5 which has a feed line 6 disposed in its lower portion for supplying expelling gas and has an overflow 8, and a separator 7 which has an otf-gas pipe 9 disposed in its upper portion. Evaporator 5 communicates with the bottom portion of reaction chamber 1 and communicates with the bottom portion of separator 7.

In reactor 1, PCl is atomized by means of nozzle 2. The atomization can be brought about with the aid of the means distributing the reaction components and including single and multi-opening nozzles and/or with the aid of a mechanical distributing or atomizing means, e.g. a rotating plate. Gases suitable for two-opening nozzles include air, N CO and other substances which do not react with the reactants. A rotating plate is most conveniently used as a mechanical atomizer. Steam is injected through feed pipe 3, and the single opening nozzle 4 can be used to convert water into mist. H PO formed in reaction chamber 1 is caused to flow into heatable evaporator 5 which is charged through pipe 6 with an inert gas, preferably air or nitrogen, and in which residual HCl and H 0 are removed. Steam in excess, hydrochloric acid, entrained H PO -droplets, residual PCl and inert gas are conveyed to separator 7, in which the H PO -droplets entrained are separated 'while residual PCl3 reacts with steam in excess to give H PO which is recycled into evaporator 5. Steam and HCl escape through off-gas line 9 into a HCl-absorption system of conventional design.

A melt of pure H31U3 is continuously discharged through overflow 8 and caused to solidify on a cooled crystallizer (not shown in the drawing).

The following examples illustrate the process of the present invention.

Example 1 2820 gram/hr. PO1 were atomized into the reactor by means of a two-opening nozzle and with the aid of 400 liter/hr. N 1540 gram/hr. steam were introduced concurrently therewith. The reaction temperature in the gas phase was ll90 C. A melt of H PO running down the reactor walls was conveyed into a heated evaporator and freed therein at 166 C. from adhering residual H 0 and HCl by causing 150 liter/hr. N to travel through the evaporator. The H PO -melt which was continuously discharged through the overflow crystallized on cooling. 1592; gram/hr. H PO corresponding to a yield of were obtained. The product contained C1 in a proportion less than 0105 P0,; in a proportion less than 1.4%, and H 0 in a proportion less than 1.5%.

Example 2 8500 gram/hr. PCl were atomized into the reactor by means of a two-opening nozzle and with the aid of 500 liter/hr. N 4330 gram/hr. steam were introduced concurrently therewith through steam supply lines. The reaction temperature in the gas phase was 188195 C. H PO running down the reactor walls was conveyed into a heated evaporator and freed therein at 187 C. from adhering residual HCl and H 0 by causing liter/hr. N to travel therethrough. The H PO -melt which was continuously discharged through the overflow crystallized on cooling. 4800 gram/hr. H PO corresponding to a yield of 94.7%, were obtained. The product contained Cl in a proportion less than 0.05%, P0; in a proportion less than 1.4%, and H 0 in a proportion less than 1.5%.

Example 3 8500 gram/ hr. PCl were atomized into the reactor by means of a two-opening nozzle and with the aid of 500 liter/hr. N 2730 gram/ hr. steam and 1040 gram/ hr. water, supplied in mist form through a single material nozzle, were introduced concurrently therewith. The reaction temperature in the gas phase was -180 C. H PO running down the reactor walls was conveyed into a heated evaporator and freed therein at C. from adhering residual water and HCl by causing 100 liter/hr. N to travel therethrough. 4830 gram/hr. H PO corresponding to a yield of 95.3%, were obtained. The product contained C1 in a proportion less than 0.05%, P0 in a proportion less than 1.4% and H 0 in a proportion less than 1.5%.

Example 4 4770 gram/hr. PCl were introduced through a feed pipe into a reactor heated at 90 C. by means of a water jacket and provided with a rotating plate in a manner such that the PCl -jet struck the plate while it rotated at a speed of about 1500 r.p.m., and became atomized. 2152 gram/hr. steam were introduced concurrently therewith through further feed pipes. The reaction temperature in the gas phase was 165-170 C. H PO running down the reactor walls was conveyed into a heated evaporator and freed therein at C. from adhering residual H 0 and HCl by causing 100 liter/hr. N to travel therethrough. 2696 gram/hr. H PO corresponding to a yield of 94.6%, were obtained. The product contained C1 in a proportion less than 0.05 PO in a proportion P0 in a proportion less than 1.4%, and H 0 in a proportion less than 1.5

We claim:

1. A process for hydrolyzing PCl to form H PO said process including the steps of spraying into a reactor a stream of steam and a stream of PCl droplets between and 500 microns in size to hydrolyze the droplets at a temperature from to 200 C., and causing the crude H PO as it is formed to drop into an evaporator where it is heated and blown with an inert gas to purify it.

2. A process for hydrolyzing PCl to form H PO in which process essentially only PC1 and Water are introduced into the vapor space of a reactor having an outlet in its lower portion, the PCl being sprayed in as a stream of droplets 50 to 500 microns large said water being at least partially introduced as a stream of steam to cause the PCl to hydrolyze at a temperature from 150 to 200 C. and to also cause the H PO so formed to drop out the reactor outlet.

3. The process of claim 1 in which the reaction temperature is between and C.

4. The process of claim 2 in which the reaction temperature is between 160 and 190 C.

5. The process of claim 1 in which a spray of liquid water is also introduced into the reactor along with the PC13 and the steam.

6. The process of claim 2 in which the P01 is sprayed in with, the help of a stream of inert gas.

References Cited UNITED STATES PATENTS 2/1954 Jones 23-165 OTHER REFERENCES J. Nassler: Collection Czech. Chem. Communications vol. 28 (12), pp. 3424-30 (1963).

OSCAR R. VERTIZ, Primary Examiner.

A. I. GREIF, Assistant Examiner.

US. Cl. X.R. 

